1. Field of the Invention
The present invention relates to a magnetoresistive element using a magnetoresistive film in which a sense current is flowed in a direction substantially perpendicular to the film surface, a magnetoresistive head using the particular magnetoresistive element, and a magnetic reproducing apparatus having the magnetoresistive head installed therein.
2. Description of the Related Art
In a certain type of a ferromagnetic material, it is known that the electrical resistance is changed in accordance with the intensity of an external magnetic field. This particular phenomenon is called the magnetoresistive effect and can be used for detecting an external magnetic field. A field-sensing element utilizing the magnetoresistive effect is called a magnetoresistive element, hereinafter referred to as an “MR element” in some cases.
The MR element is utilized in a magnetic head for reading information stored on a magnetic recording medium in a magnetic reproducing apparatus utilizing a magnetic recording medium such as a hard disk or a magnetic tape, and the particular magnetic head is called an MR head.
In recent years, magnetic recording density is being made higher in the magnetic recording-reproducing apparatus utilizing the MR head, particularly, in a hard disk apparatus, with the result that the size of one bit is being made smaller and the leakage magnetic flux from the bit, i.e., the signal magnetic field, is being made lower. Such being the situation, an MR element of high sensitivity and a high signal-to-noise ratio, which is capable of providing a high magnetoresistive ratio even under a lower magnetic field, is required for reading information written on a magnetic recording medium with a high density.
Under the circumstances, a giant magnetoresistive element (GMR element), i.e., a so-called “spin-valve film”, that permits to provide a high MR ratio is generally used nowadays as the MR element included in the hard disk MR head.
The spin-valve film has a stacked structure comprising a ferromagnetic layer F, a non-magnetic layer S, a ferromagnetic layer P, and an antiferromagnetic layer, which are stacked in the order mentioned. The ferromagnetic layer P and the ferromagnetic layer F are in a magnetically non-coupled state with the nonmagnetic layer S interposed therebetween. The magnetization of the ferromagnetic layer P is pinned by the exchange bias with the antiferromagnetic material, and the magnetization of the ferromagnetic layer F can be easily rotated by, for example, an external magnetic field (e.g., an signal magnetic field). It is possible to obtain a high magnetoresistive effect by allowing the magnetization of the ferromagnetic layer F alone to be rotated by the external magnetic field so as to change the relative angle made between the magnetization directions of the two ferromagnetic layers.
The ferromagnetic layer F may be referred to as a free layer, a field-sensing layer or a magnetization free layer. The ferromagnetic layer P may be referred to as a pinned layer or a magnetization pinned layer. The nonmagnetic layer S may be referred to as a spacer layer, an interface regulating intermediate layer or an intermediate layer.
In the GMR head widely used nowadays, employed in general is a system in which a sense current is flowed in a direction parallel to the film surface to measure the resistance in the direction parallel to the film surface. This system is generally called a current-in-plane (CIP) system. In the case of the CIP system, it is possible to obtain an MR ratio of about 10 to 20%. However, it is expected that an even higher MR ratio be required in order to achieve reproduction at a high recording density exceeding 200 Gbit/inch2. On the other hand, it is difficult to obtain an MR ratio exceeding 20% when it comes to the CIP spin-valve film available nowadays. As a result, the situation as to how much the MR ratio can be increased is a serious problem that must be solved for further improving the recording density.
Under the circumstances, a current-perpendicular-to-plane (CPP) GMR film, which is generally said to exhibit an MR ratio higher than that of the CIP-GMR film, is attracting attention. In the CPP system, a sense current is flowed in a direction perpendicular to the film surface. However, in the CPP-GMR film, the resistance of the portion corresponding to the thickness of the GMR film is to be measured and, thus, the unit-area resistance is made very low. As a result, the output as the resistance of the element is very low so as to give rise to a problem that it is impossible to obtain a high signal-to-noise ratio.
In order to overcome the aforementioned problems of the low resistance and the low MR ratio, a CPP-GMR element provided with a resistance adjustment layer having a current confining effect is proposed in, for example, U.S. Pat. No. 6,348,274. In this prior art, however, the interlayer coupling (Hin) between the free layer and the pinned layer is made prominent so as to give rise to a problem that the breakdown voltage is lowered.